1. Field of the Invention
The invention relates to magneto-optic garnet materials having applications in optical devices such as isolators, circulators and interleavers.
2. Discussion of the Related Art
Co-assigned U.S. Pat. Nos. 5,608,570 and 5,801,875, the disclosures of which are hereby incorporated by reference, disclose magneto-optic garnet materials useful for Faraday rotator applications. As discussed therein, the disclosed materials exhibit highly desirable magnetic properties, including a substantially rectangular magnetization loop, relatively low saturation magnetization over a useful operating temperature range, and a relatively high switching field at least at room temperature. (FIG. 1 is representative of the properties of these materials.) These materials are referred to generally as latching garnet materials, due to their ability to remain in a magnetically saturated (i.e., single domain) state. However, the garnet materials disclosed in the above patents exhibited particularly advantageous properties, due to their ability to remain latched over a relatively broad temperature range, and their ability to be xe2x80x9chardxe2x80x9d latched.
(As used herein: magnetization loop is the curve of magnetization vs. applied magnetic field; a magnetization loop is xe2x80x9csubstantially rectangularxe2x80x9d if the width of the magnetization reversal is at most 10 Oe; the xe2x80x9cswitching fieldxe2x80x9d (Hs) of the magnetization loop is the applied field at which the magnetization goes through zero (Hs corresponds to the coercive fieldxe2x80x94Hc of a conventional magnetization loop; xe2x80x9chard latchingxe2x80x9d means a switching field of 500 Oe or greater at least at room temperature.)
While the materials of the above-cited patents exhibit excellent properties, improvements in the materials and the processes for making the materials and articles incorporating the materials are always desired.
The invention relates to improvements in the production of high-performance latching magneto-optic garnet materials. It has been recognized that high-Europium magneto-optic garnets will offer superior properties in devices such as isolators, circulators and interleavers. However, formation of, e.g., (BiEu)3(FeGa)5O12 on conventional, congruent composition, garnet substrates is difficult, due to poor lattice matching between the magneto-optic garnet and such conventional substrates. The invention addresses this problem.
The invention involves a process for forming an article, the process including steps of providing a substrate, and forming on the substrate a film of (BiEu)3(Fe5xe2x88x92y(GaxAl1xe2x88x92x)y)O12, where x is 0 to 1, and y is 0.8 to 1.2 (with y generally selected such that the film exhibits a saturation magnetization less than 100 G at room temperature). According to one aspect of the invention, the substrate is a single crystal material consisting essentially of a solid solution of two or more garnet materials, the substrate having a lattice parameter within 0.004 Angstrom of the lattice parameter of the (BiEu)3(Fe5xe2x88x92y(GaxAl1xe2x88x92x)y)O12, advantageously within 0.002 Angstrom, more advantageously within 0.001 Angstrom. By use of a solid solution of two or more garnets, e.g., two congruent garnet compositions, an acceptable lattice parameter is able to be attained. In another aspect, the substrate is a single crystal material consisting essentially of a solid solution of gadolinium scandium gallium garnet and gadolinium scandium aluminum garnet, or a solid solution of gadolinium scandium gallium garnet and terbium scandium gallium garnet. These combinations, in proper compositional ratios, are able to provide lattice parameters that facilitate formation of desirable, high-Eu magneto-optic garnets.
Garnets of the above formula in which x is 1 tend to provide highly desirable magnetic properties. Inclusion of aluminum is useful in some cases, however, because even a small amount of aluminum can modify the lattice parameter to an extent that widens the range of potential substrate materials.